标题： X 射线天文台 ULLYSES：低金属丰度的大质量恒星。 第 XIII 部分：在大麦哲伦云中检验双稳态跃迁。 显示英文标题

标题： X-Shooting ULLYSES: Massive stars at low metallicity. XIII. Putting the bi-stability jump to the test in the LMC

摘要： 我们旨在研究理论上的双稳态跃迁，该跃迁预测了低于21千开尔文时质量损失率的增加。 我们进一步的目标是限制16颗大麦哲伦云晚期O型和B型超巨星的大气和风参数。 我们利用基于网格的1D非局部热平衡辐射传输模型CMFGEN以及随后的精细光谱拟合程序来确定每颗恒星的恒星和风参数。 我们将这种方法应用于ULLYSES计划的紫外数据和XShootU合作的互补光学数据。 我们还利用演化模型来获得演化质量和与我们的光谱质量进行比较。 我们推导出16颗跨度广泛的晚期O型和B型超巨星的物理参数和风特性，温度范围为12-30千开尔文（$T_{eff}$），表面重力范围为1.8-3.1（$\log{g/cm~s^{-2}}$），质量损失率范围为$10^{-7.6}-10^{-5.7}M_{\odot}yr^{-1}$。 我们还将结果与其他LMC OB型恒星的光谱研究进行了对比。 我们发现我们得出的大气和风特性与多个先前的研究一致。 对于我们的大多数样本，我们发现演化质量和光谱质量是一致的。 我们的结果在任何温度范围内都没有再现双稳态跃迁，而是发现在较低温度下质量损失率呈单调下降。 我们获得了LMC超巨星的终端风速-有效温度关系。 我们发现我们得出的质量损失率与任何数值配方的预测都不一致。 终端风速与逃逸速度的比值也是如此（$v_{\infty}/v_{esc}$），我们得出了$v_{\infty}/v_{esc}$-$T_{eff}$关系。 通过与先前SMC研究的比较，我们发现风特性依赖于金属丰度，并得到了一个新的修正的风动量-光度关系。 显示英文摘要

摘要： We aim to investigate the theoretical bi-stability jump, which predicts an increase in mass-loss rates below 21 kK. We further aim to constrain the photospheric and wind parameters of a sample of 16 LMC late-O and B supergiants. We utilise the 1D, non-LTE radiative transfer model CMFGEN in a grid-based approach and subsequent fine-tuned spectroscopic fitting procedure to determine the stellar and wind parameters of each star. We apply this method to ultra-violet data from the ULLYSES programme and complementary optical data from the XShootU collaboration. We also utilise evolutionary models to obtain the evolutionary masses and compare them to our derived spectroscopic masses. We derive physical parameters and wind properties of 16 late-O and B supergiants that span a wide $T_{eff}$ range of 12-30 kK, surface gravity range $\log{g/cm~s^{-2}}$ of 1.8-3.1, and a mass-loss rate range of $10^{-7.6}-10^{-5.7}M_{\odot}yr^{-1}$. We also compare our results to previous studies spectroscopic studies of LMC OB stars. We find that our derived photospheric and wind properties are consistent with multiple previous studies. For most of our sample, we find that the evolutionary masses and spectroscopic masses are consistent. Our results do not reproduce a bi-stability jump in any temperature range, but rather a monotonic decrease in mass-loss rate at lower temperatures. We obtain a terminal wind velocity-effective temperature relation for LMC supergiants. We find that our derived mass-loss rates do not agree with predictions from any of the numerical recipes. This is also the case for the ratio of the terminal wind velocity to the escape velocity $v_{\infty}/v_{esc}$, and we derive a $v_{\infty}/v_{esc}$-$T_{eff}$ relation. We find that wind properties are metallicity dependent from a comparison with a previous SMC study, and we obtain a new modified wind momentum-luminosity relation.